Hexagonal boron nitride powder and method for producing the same

Abstract

There is provided a hexagonal boron nitride powder, having: an average long diameter (L50) of 3 to 20 μm, an average thickness (T50) of 0.3 to 2 μm, a (L90−L10)/L50 of 2.0 or less, a (T90−T10)/T50 of 2.0 or less, and an average aspect ratio of 10 to 30; a dynamic friction coefficient (MIU) of 0.50 or less, and a deviation of the dynamic friction coefficient (MMD) of 0.0050 or less; and a specular reflection intensity of 80 or more as measured by a goniophotometer under a condition of an angle of incidence of 60° C.

1 . A hexagonal boron nitride powder, having:
 an average long diameter (L50) of 3 to 20 μm, an average thickness (T50) of 0.3 to 2 μm, a (L90−L10)/L50 of 2.0 or less, a (T90−T10)/T50 of 2.0 or less, and an average aspect ratio of 10 to 30;   a dynamic friction coefficient (MIU) of 0.50 or less, and a deviation of the dynamic friction coefficient (MMD) of 0.0050 or less; and   a specular reflection intensity of 80 or more as measured by a goniophotometer under a condition of an angle of incidence of 60°.   
     
     
         2 . The hexagonal boron nitride powder according to  claim 1 , wherein the (L90−L10)/L50 is 1.8 or less. 
     
     
         3 . The hexagonal boron nitride powder according to  claim 1 , for use in a cosmetic. 
     
     
         4 . A cosmetic including the hexagonal boron nitride powder according to  claim 1 . 
     
     
         5 . A method for producing a hexagonal boron nitride powder, including reducing and nitriding a raw material mixture by heating in a nitrogen atmosphere, wherein
 the raw material mixture contains an oxygen-containing boron compound, an oxygen-containing alkaline earth metal compound, a carbon source, and a seed crystal, and   the seed crystal is a boron nitride powder with a specific surface area of 10 m 2 /g or more obtained by subjecting a raw material boron nitride powder with a graphitization index of 1.7 or less to wet-type jet milling.   
     
     
         6 . The method for producing a hexagonal boron nitride powder according to  claim 5 , wherein the raw material boron nitride powder to be subjected to wet-type jet milling is in the form of a slurry with a density of 20 to 100 g/L. 
     
     
         7 . The method for producing a hexagonal boron nitride powder according to  claim 5 , wherein the raw material mixture has:
 an atomic ratio (B/C ratio) of boron atoms (B) in the oxygen-containing boron compound to carbon atoms (C) in the carbon source of 0.70 to 2.00;   a molar ratio (AO/B 2 O 3  ratio) of the oxygen-containing alkaline earth metal compound (AO; A is an alkaline earth metal) to the oxygen-containing boron compound (B 2 O 3 ) of 0.01 to 1.0 in terms of oxide; and   an atomic ratio (B S /C ratio) of boron atoms (B S ) in the boron nitride powder as the seed crystal to the carbon atoms (C) in the carbon source of 0.01 to 13.   
     
     
         8 . The method for producing a hexagonal boron nitride powder according to  claim 5 , wherein the raw material mixture is reduced and nitrided by heating at a temperature of 1700° C. to 2100° C.